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\KOMAProvidesFile{scrlayer.tex}
                 [$Date: 2019-12-06 12:04:10 +0100 (Fri, 06 Dec 2019) $
                  KOMA-Script guide (chapter:scrlayer)]

\translator{Markus Kohm\and Karl Hagen}

% Date of the translated German file: 2019-12-03

\chapter[{Defining Layers and Page Styles with \Package{scrlayer}}]
  {Defining\ChangedAt{v3.12}{\Package{scrlayer}} Layers and Page Styles with
	\Package{scrlayer}}
\labelbase{scrlayer}

\BeginIndexGroup
\BeginIndex{Package}{scrlayer}%
\BeginIndex{}{layer}%
Most users of graphics software are already familiar with the layer model for
a page. Such a model is rather alien to \LaTeX{} itself, but some packages,
like \Package{eso-pic} or \Package{textpos}, provide a kind of
background or foreground layer. \Package{scrlayer} is another package that
provides such background and foreground layers, but unlike the packages
mentioned above, these layers are part of the page style. As a result, you can
switch between different layers simply by switching the page style.

To do so, the package also supports a low-level interface for defining page
styles that are based on a stack or list of layers, for adding layers to such
a layer stack, either at the top or the bottom, or before or after a specific
layer, and for removing individual layers and duplicates from a stack. In a
nutshell, the page style interface of \Package{scrlayer} provides commands to
define page styles based on a stack of layers and to manage those stacks.

Nevertheless, using the layers directly is recommended for advanced users
only. Interfaces for beginners and average users are provided by additional
packages that in turn load \Package{scrlayer}. See
\autoref{cha:scrlayer-scrpage} in \autoref{part:forAuthors} of this
\iffree{manual}{book}.


\LoadCommonFile{options} % \section{Early or Late Selection of Options}

\section{Generic Information}
\seclabel{generic.information}

The package needs some generic information about the class being used. Class
authors can help \Package{scrlayer} by providing the appropriate information.
Otherwise the package will try to determine this information for itself. This
works, for example, for the standard and the \KOMAScript{} classes. It may
work with other classes, or it may fail in whole or in part.

This section describes some of the information that class authors can provide.
Normally, users should not have to worry about it.

\begin{Declaration}
  \Macro{if@chapter}\ \PName{then code}\ \textMacro{else}\ %
  \PName{else code}\ \textMacro{fi}%
\end{Declaration}
If \Macro{if@chapter} is defined and corresponds to
\Macro{iftrue}\IndexCmd{iftrue}, \Package{scrlayer} takes the chapter level
into account when, for example, processing the
\DescRef{\LabelBase.option.automark} option. If it is defined but is not
\Macro{iftrue}, \Package{scrlayer} handles only the
\DescRef{maincls.cmd.part}, \DescRef{maincls.cmd.section},
\DescRef{maincls.cmd.subsection}, \Macro{sub\dots subsection},
\DescRef{maincls.cmd.paragraph}, \DescRef{maincls.cmd.subparagraph},
\Macro{sub\dots subparagraph} sectioning units. If the macro is undefined,
\Package{scrlayer} searches for \DescRef{maincls.cmd.chapter}. If
\DescRef{maincls.cmd.chapter} is defined and does not correspond to
\Macro{relax}, \Package{scrlayer} defines \Macro{if@chapter} to
\Macro{iftrue}. Otherwise \Macro{if@chapter} becomes
\Macro{iffalse}\IndexCmd{iffalse}.%
\EndIndexGroup


\begin{Declaration}
  \Macro{if@mainmatter}\ \PName{then code}\ %
  \textMacro{else}\ \PName{else code}\ \textMacro{fi}%
\end{Declaration}
Classes like \Class{book} or \Class{scrbook} provide
\DescRef{maincls.cmd.frontmatter}\IndexCmd{frontmatter},
\DescRef{maincls.cmd.mainmatter}\IndexCmd{mainmatter}, and
\DescRef{maincls.cmd.backmatter}\IndexCmd{backmatter} to switch between the
front, main, and end parts of a book. Typically, these classes also use
\Macro{if@mainmatter} internally to decide whether the current text is part of
the main body of the document or not. Classes like \Class{report} and
\Class{article} have no \DescRef{maincls.cmd.frontmatter},
\DescRef{maincls.cmd.mainmatter}, or \DescRef{maincls.cmd.backmatter} and
therefore also lack \Macro{if@mainmatter}.

It is easier for \Package{scrlayer} to avoid constantly testing for the
existence of these commands to decide whether to work in the main matter or
not, and instead to use  \Macro{if@mainmatter}\IndexCmd{iftrue} with classes
like \Class{report} and \Class{article}. So if \Macro{if@mainmatter} is not
defined, \Package{scrlayer} defines it as a synonym for \Macro{iftrue}.

Some classes, however, define \DescRef{maincls.cmd.frontmatter},
\DescRef{maincls.cmd.mainmatter}, or \DescRef{maincls.cmd.backmatter} but not
\Macro{if@mainmatter}. In this case, \Package{scrlayer} also defines
\Macro{if@mainmatter} to be \Macro{iftrue} and it extends definition of
\DescRef{maincls.cmd.frontmatter}, \DescRef{maincls.cmd.mainmatter}, and
\DescRef{maincls.cmd.backmatter} to set \Macro{if@mainmatter} properly.
However, if there are other, comparable commands for switching between
different document parts. \Package{scrlayer} will not recognize them, does not
test for them, and therefore cannot extend them appropriately. In this case,
\Package{scrlayer} needs help of the class author to set \Macro{if@mainmatter}
correctly.%
\EndIndexGroup


\begin{Declaration}
  \Macro{DeclareSectionNumberDepth}\Parameter{level name}%
                                   \Parameter{level depth}
\end{Declaration}
Generally each section level is assigned an integer number indicating its
depth in the document structure. \LaTeX{} needs this to manage the hierarchy
of the section levels. But normally these values are known only to the
particular class that defines the section commands. This class then uses the
appropriate numbers inside the corresponding commands.

The \Package{scrlayer} package also needs information about the section
hierarchy. With the help of \Macro{DeclareSectionNumberDepth}, you can map the
name of a heading level to a corresponding \PName{level depth}. For example,
for the standard \Class{book} class, the \PName{level name}s would be
\PValue{part}, \PValue{chapter}, \PValue{section}, \PValue{subsection},
\PValue{subsubsection}, \PValue{paragraph}, and \PValue{subparagraph}, and the
corresponding \PName{level depth}s would be -1, 0, 1, 2, 3, 4, and 5.

The \Package{scrlayer} package tries to determine the \PName{level depth}s on
its own while loading and again during \Macro{begin}\PParameter{document}. But
if this fails, for example because you use completely different sectioning
commands, you can define the relationship explicitly with
\Macro{DeclareSectionNumberDepth}.%
\EndIndexGroup


\section{Declaring Layers}
\seclabel{layers}

A layer is an abstract model of a page. Unlike a real, physical sheet of
paper, this page is completely transparent. Typically, multiple layers are
stacked atop one another and opaque material on one layer hides material on
the layers below. The stack of layers is then merged to form the physical
page. The \Package{scrlayer} package provides two such stacks for each page: a
background stack and a foreground stack. The background stack is printed
beneath the normal page content, while the foreground stack is printed above
it. The normal page content is therefore a kind of a dividing layer between
the two layer stacks.

A layer has several attributes that can be understood as answers to some basic
questions:
\iffree{\begin{description}}{%
    \begingroup
    \RedeclareSectionCommand[beforeskip=.5\baselineskip plus .25\baselineskip
    minus .1\baselineskip]{paragraph}%
    \renewcommand*\item[4][]{\paragraph*{#3{#4}#1}}%
  }%
\item[Does the layer belong to the foreground or the background?]%
  \leavevmode\textnote{foreground or background}\hskip 0pt
  Background layers are output before the normal content of the page.
  Therefore they appear behind or beneath the normal content of the page.
  Foreground layers are then output after the normal content. Therefore they
  appear on top of the normal content of the page. By default, a layer is both
  a background layer \emph{and} a foreground layer and therefore is printed
  twice. Usually it makes sense to limit the layer explicitly to either the
  foreground or the background.
\item[What is the position of the layer?]%
  \leavevmode\textnote{horizontal and vertical position}\hskip 0pt
  To answer this question, there are attributes to define the layer's 
  horizontal and vertical position.
\item[How big is the layer?\textnote{horizontal and vertical size}]%
  As with the position, there are also attributes to define the width and
  height of a layer. Thus a layer can be smaller or larger than the paper
  and it can be placed at different positions on the paper.
\item[How are the horizontal and vertical positions measured?]%
  \leavevmode\textnote{alignment}\hskip 0pt
  This question is answered by the alignment attribute. The horizontal 
  position can be measured from the left edge of the paper to the left edge of
  the layer, to the centre of the layer, to the right edge of the layer. 
  Similarly, the vertical position can be measured from the top edge of the
  paper to the top edge of the layer, the centre of the layer, or the bottom
  edge of the layer.
\item[Is the layer intended for text or picture output?]%
  \leavevmode\textnote{text or	picture}\hskip 0pt
  This question is closely related to the position. For example, users often
  expect the origin for a picture to be at the lower left corner of the layer.
  But this would not be suitable for text output. Therefore the origin of a 
  text layer is the height of a standard text line below the top left corner 
  of the layer. Picture layers, on the other hand, create a
  \Environment{picture}\IndexEnv{picture} environment in which additional
  positioning commands are available.
\item[Should the layer be printed on left or right pages?]%
  \leavevmode\textnote{left or right page}\hskip 0pt
  By default a layer will be printed on all pages. Note that \LaTeX{} treats
  even pages as left-side pages and odd pages as right-side pages, but in
  one-sided printing, only right-hand pages exist regardless of the page
  number.
\item[Should the layer be printed in one-sided or two-sided mode?]%
  \leavevmode\textnote{one-sided or two-sided}\hskip 0pt
  By default a layer will be printed in both one-sided and two-sided
  printing. Nonetheless, a layer that is restricted to even pages will never
  be printed in one-sided printing and therefore is not a one-sided layer.
\item[Should the layer be printed on float pages or normal pages?]%
  \leavevmode\textnote{float page or normal page}\hskip 0pt
  \LaTeX{} produces float pages for objects from environments like tables or 
  figures if they are allowed to appear on a page without normal page contents
  (see option \PValue{p} for \Environment{figure} or \Environment{table}). In 
  effect, the entire page is allowed to float within the document. Normal
  pages in this sense are all pages that are not float pages. Normal pages can
  also contain floats at the top, in the middle, or at the bottom of the page.
  Very large floats can give the impression of being page floats, while in 
  reality they are floating environments placed at the top of a normal page.
\item[What are the contents of the layer?]%
  \leavevmode\textnote{contents}\hskip 0pt
  The corresponding attribute simply contains what should be printed whenever
  the layer is output.
\iffree{\end{description}}{%
  \endgroup\par\bigskip\noindent\ignorespaces
}%
These eight questions immediately give rise to a number of attributes. Later
\iffree{in this guide}, we will describe additional attributes. However, they
are only defined for convenience and can be expressed by a combination of
these primary attributes.


\begin{Declaration}
  \Macro{DeclareLayer}\OParameter{option list}\Parameter{layer name}%
  \Macro{DeclareNewLayer}\OParameter{option list}\Parameter{layer name}%
  \Macro{ProvideLayer}\OParameter{option list}\Parameter{layer name}%
  \Macro{RedeclareLayer}\OParameter{option list}\Parameter{layer name}%
  \Macro{ModifyLayer}\OParameter{option list}\Parameter{layer name}
\end{Declaration}
These commands can be used to define layers. The \PName{layer name} must be
fully expandable and should expand to ASCII letters only. Some additional
characters are accepted, but their use is only recommended for advanced users.

The \Macro{DeclareLayer} command does not care whether or not a layer with the
given \PName{layer name} already exists. It will under all circumstances
define the layer with the attributes specified in the \PName{option list}. An
\PName{option} can be either a key or a key followed by an equal sign and
a value. Multiple options are separated by commas. To use a comma or a white
space within the value of an option, you must put the value inside curly
brackets. See \autoref{tab:scrlayer.layerkeys} for more information on keys,
values, and the corresponding attributes.

Unlike \Macro{DeclareLayer}, \Macro{DeclareNewLayer} reports an error if a 
layer with the same \PName{layer name} already exists. This prevents the user
from accidentally using the same \PName{layer name} more than once. This 
is especially useful when classes or packages also define layers internally.

In contrast, \Macro{ProvideLayer} only defines a layer if there is no layer 
with the same name already. If the name is in use for another layer, the new 
definition is ignored. Therefore this command has the meaning, \emph{define
	the layer only if it does not already exist.}

If you want to redefine an existing layer, you can use \Macro{RedeclareLayer} 
or \Macro{ModifyLayer}. With \Macro{RedeclareLayer}, the layer is first reset
to the default settings and then completely redefined via the specified 
options list. In contrast, \Macro{ModifyLayer} does not reset the layer.
Only those attributes which are explicitly set in the \PName{option list} will
be changed. Applying either command to a previously undefined \PName{layer 
	name} results in an error.

\begin{desclist}
  \desccaption{%
    Options for defining page layers and the meaning of the
    corresponding layer attribute\label{tab:scrlayer.layerkeys}%
  }{%
    Options for defining layers (\emph{continued})%
  }%
  \entry{%
    \ChangedAt{v3.16}{\Package{scrlayer}}%
    \OptionVName{addcontents}{Code}}{%
    The specified \PName{code} will be appended to the current value of the
    \Option{contents} attribute, so the new content will appear at the end of
    the existing content. For more information about the handling of 
    \PName{code} see the \Option{contents} option.%
  }%
  \entry{%
    \ChangedAt{v3.16}{\Package{scrlayer}}%
    \OptionVName{addheight}{additional height}}{%
    The current value of the \Option{height} attribute will be increased by 
    the value of this option. You can use the same kind of values as for
    \Option{height}.%
  }%
  \entry{%
    \ChangedAt{v3.16}{\Package{scrlayer}}%
    \OptionVName{addhoffset}{additional horizontal offset}}{%
    The current value of the \Option{hoffset} attribute will be increased by 
    the value of this option. You can use the same kind of values as for
    \Option{hoffset}.%
  }%
  \entry{%
    \ChangedAt{v3.16}{\Package{scrlayer}}%
    \OptionVName{addvoffset}{additional vertical offset}}{%
    The current value of the \Option{voffset} attribute will be increased by 
    the value of this option. You can use the same kind of values as for
    \Option{voffset}.%
  }%
  \entry{%
    \ChangedAt{v3.16}{\Package{scrlayer}}%
    \OptionVName{addwidth}{additional width}}{%
    The current value of the \Option{width} attribute will be increased by 
    the value of this option. You can use the same kind of values as for
    \Option{width}.%
  }%
  \nentry{\KOption{align}{\PName{alignment characters}}}{%
    The \PName{alignment characters} define the desired alignment of the
    layer. Each \PName{alignment character} determines how the \PName{length}
    of either the \Option{hoffset} or the \Option{voffset} option is 
    interpreted. Multiple \PName{alignment character}s can be used together 
    (without spaces or commas) and are evaluated in the order they occur. 
    Macros are not permitted in the value of the option. Valid 
    \PName{alignment character}s are:
    \begin{description}
    \item[\PValue{b} --] align the layer at its bottom edge; the value of
      \Option{voffset} is the distance from the top edge of the paper to the
      bottom of the layer.
    \item[\PValue{c} --] align the layer at its centre; the values of
      \Option{voffset} and \Option{hoffset} are interpreted as the distance
      from the top left corner of the paper to the centre of the layer.
    \item[\PValue{l} --] align the layer at its left edge; the value of
      \Option{hoffset} is interpreted as the distance from the left edge of
      the paper to the left edge of the layer.
    \item[\PValue{r} --] align the layer at its right edge; the value of
      \Option{hoffset} is interpreted as the distance from the left edge of
      the paper to the right edge of the layer.
    \item[\PValue{t} --] align the layer at its top edge; the value of
      \Option{voffset} is interpreted as the distance from the top edge of the
      paper to the top edge of the layer.
    \end{description}%
  }%
  \entry{\KOption{area}{%
      \Parameter{hoffset}\Parameter{voffset}%
      \Parameter{width}\Parameter{height}}}{%
    This composite option sets the primary attributes
    \OptionValue{hoffset}{horizontal offset}, \OptionValue{voffset}{vertical
      offset}, \OptionValue{width}{width}, \OptionValue{height}{height}.%
  }%
  \entry{\ChangedAt{v3.18}{\Package{scrlayer}}%
    \Option{backandforeground}}{%
    This option removes the restriction of a layer to the foreground or the
    background. In general, this option makes little sense, but it is provided
    for the sake of a complete user interface. This option does not expect or
    allow a value.%
  }%
  \entry{\Option{background}}{%
    This option displays the layer in the background only. The default is to
    display layers in both the background and the foreground. This option does
    not expect or allow a value.%
  }%
  \entry{\Option{bottommargin}}{%
    This composite option sets the primary attributes \Option{hoffset},
    \Option{voffset}, \Option{width}, \Option{height}, and \Option{align} so
    that the layer spans the paper horizontally from the left edge to the
    right and vertically from immediately beneath the footer to the bottom
    edge of the paper.%
  }%
  \entry{\KOption{clone}{\PName{layer name}}}{%
    This composite option sets all primary attributes of the layer to the same
    values as the primary attributes of the layer with the given \PName{layer
      name}. See the notes on the \PName{layer name} at the beginning of the
    explanation for \Macro{DeclareLayer}. The layer to be cloned must also
    already exist.%
  }%
  \entry{\KOption{contents}{\PName{code}}}{%
    The specified \PName{code} will be expanded whenever the layer is printed.
    This \PName{code} defines what you see for the layer. No tests are made to
    see if the code is valid. Errors in the \PName{code} can therefore lead to
    multiple error messages on each page that prints the layer.%
  }%
  \entry{\Option{evenpage}}{%
    This option causes the layer to appear on even pages only, unlike the
    default, where a layer will appear on both even and odd pages. Since even
    pages only appear in two-sided printing, this option implies
    \Option{twoside}. This option does not expect or allow a value.%
  }%
  \entry{\ChangedAt{v3.18}{\Package{scrlayer}}%
    \Option{everypage}}{%
    This option is a combination of \Option{oddorevenpage} and
    \Option{floatornonfloatpage}. This option does not expect or allow a
    value.%
  }%
  \entry{\Option{everyside}}{%
    This option removes any restriction of the layer to one-sided or two-sided
    printing. This is the default setting. This option does not expect or
    allow a value.%
  }%
  \entry{\ChangedAt{v3.18}{\Package{scrlayer}}%
    \Option{floatornonfloatpage}}{%
    This option removes any restriction of the layer to float or non-float
    pages and restores the default setting. This option does not expect or
    allow a value.%
  }%
  \entry{\Option{floatpage}}{%
    This option restricts the layer to appearing on float pages only. The
    default setting is for layers to appear on both float and non-float pages.
    This option does not expect or allow a value.%
  }%
  \entry{\Option{foot}}{%
    This composite option sets \Option{hoffset}, \Option{voffset},
    \Option{width}, \Option{height}, and \Option{align} so that the layer
    spans the page footer over the width of the text area. This option does
    not expect or allow a value.%
  }%
  \entry{\Option{footskip}}{%
    This composite option sets \Option{hoffset}, \Option{voffset},
    \Option{width}, \Option{height}, and \Option{align} so that the layer
    spans the vertical distance between the text area and the page footer over
    the width of the text area. Note, however, that although the height of
    this area depends on \Length{footskip}, it is not the same. This option
    does not expect or allow a value.%
  }%
  \entry{\Option{foreground}}{%
    This option displays the layer in the foreground only. The default is to
    display layers in both the background and the foreground. The option does
    not expect or allow a value.%
  }%
  \entry{\Option{head}}{%
    This composite option sets \Option{hoffset}, \Option{voffset},
    \Option{width}, \Option{height}, and \Option{align} so that the layer
    spans the vertical area of the page header for the width of the text area.
    The height corresponds to the length \Length{headheight}. This option does
    not expect or allow a value.%
  }%
  \entry{\Option{headsep}}{%
    This composite option sets \Option{hoffset}, \Option{voffset},
    \Option{width}, \Option{height}, and \Option{align} so that the layer
    spans the vertical distance between the page header and the text area for
    the width of the text area. The height corresponds to the length
    \Length{headsep}. This option does not expect or allow a value.%
  }%
  \entry{\KOption{height}{\PName{length}}}{%
    Sets the height of the layer. Note that the \PName{length} can be a
    \LaTeX{} length declared with \Macro{newlength}, a \TeX{} length declared
    with \Macro{newdimen} or \Macro{newskip}, a length value like 10\,pt, or a
    dimensional expression using +, -, /, *, (, and ). For more information
    about valid dimensional expressions see \cite[section~3.5]{manual:eTeX}.%
  }%
  \entry{\KOption{hoffset}{\PName{length}}}{%
    Sets the distance of the layer from the left edge of the paper. How the
    distance is measured depends on the \Option{align} option. See the
    \Option{height} option for more information about valid expressions for
    \PName{length}.%
  }%
  \entry{\Option{innermargin}}{%
    This composite option sets \Option{hoffset}, \Option{voffset},
    \Option{width}, \Option{height}, and \Option{align} so that the layer
    spans the inner margin, from the edge of the page to the edge of the text
    area and from the top to the bottom of the page. In one-sided printing,
    the inner margin corresponds to the left margin. This option does not
    expect or allow a value.%
  }%
  \entry{\Option{leftmargin}}{%
    This composite option sets \Option{hoffset}, \Option{voffset},
    \Option{width}, \Option{height}, and \Option{align} so that the layer
    spans the left margin, from the left edge of the paper to the left edge of
    the text area and from the top of the paper to the bottom. This option
    does not expect or allow a value.%
  }%
  \entry{\ChangedAt{v3.19}{\Package{scrlayer}}%
    \OptionVName{mode}{mode}}{%
    This primary option defines the \PName{mode} in which the layer's content
    is output. The default is \OptionValue{mode}{text}. The baseline of the
    first text line is placed the height of one standard text line below the
    top edge of the layer, so the text is usually neatly aligned with the top
    of the layer. In \PValue{picture} \PName{mode}, on the other hand, the
    layer spans a \Environment{picture} environment with the origin at the
    bottom left corner of the layer. The \PValue{raw} \PName{mode} is also
    also defined. By default it corresponds to \PValue{text} \PName{mode}.
    Changing\textnote{Attention!} the \PName{mode} of a layer usually results
    the contents shifting. Furthermore, the \PValue{picture} \PName{mode}
    provides additional commands that result in errors with another
    \PName{mode}. Therefore it usually makes no sense to change the
    \PName{mode} of a layer after its initial declaration!%
  }%
  \entry{\Option{nonfloatpage}}{%
    This option restricts the layer to pages that are not float pages. The
    default is for the layer to appear on both float and non-float pages. This
    option does not expect or allow a value.%
  }%
  \entry{\ChangedAt{v3.18}{\Package{scrlayer}}%
    \Option{oddorevenpage}}{%
    This option removes any restriction of the layer to odd or even pages,
    restoring the default behaviour that the layer should appear on both odd
    and even pages. The option does not expect or allow a value.%
  }%
  \entry{\Option{oddpage}}{%
    This option restricts the layer to odd pages only. The default is for
    layers to appear on both odd pages and on even pages. Note that in
    one-sided printing, all pages are odd, regardless of the page number. This
    option does not expect or allow a value.%
  }%
  \entry{\Option{oneside}}{%
    This option restricts the layer to one-sided printing only. The default is
    for layers to appear in both one-sided and two-sided printing. This option
    does not expect or allow a value.%
  }%
  \entry{\Option{outermargin}}{%
    The composite option sets \Option{hoffset}, \Option{voffset},
    \Option{width}, \Option{height}, and \Option{align} so that the layer
    spans the outer margin of the page, from the top to the bottom of the
    paper. The outer margin corresponds to the right margin in one-sided
    printing. This option does not expect or allow a value.%
  }%
  \entry{\Option{page}}{%
    This composite option sets \Option{hoffset}, \Option{voffset},
    \Option{width}, \Option{height}, and \Option{align} so that the layer
    spans the the whole paper. This option does not expect or allow a value.%
  }%
  \entry{\ChangedAt{v3.16}{\Package{scrlayer}}%
    \OptionVName{pretocontents}{code}}{%
    The value of \PName{code} is prefixed the current value of the
    \Option{contents} attribute, so the new content will appear before the
    existing content. For more information about the handling of \PName{code},
    see the \Option{contents} option.%
  }%
  \entry{\Option{rightmargin}}{%
    This composite option sets \Option{hoffset}, \Option{voffset},
    \Option{width}, \Option{height}, and \Option{align} so that the layer
    spans the right margin, from the right edge of the text area to the right
    edge of the paper and from the top to the bottom edge of the paper. This
    option does not expect or allow a value.%
  }%
  \entry{\Option{textarea}}{%
    This composite option sets \Option{hoffset}, \Option{voffset},
    \Option{width}, \Option{height}, and \Option{align} so that the layer
    spans the entire text area. This option does not expect or allow a value.%
  }%
  \entry{\Option{topmargin}}{%
    This composite option sets \Option{hoffset}, \Option{voffset},
    \Option{width}, \Option{height}, and \Option{align} so that the layer
    spans the vertical distance between the top edge of the paper to the
    header for the entire width of the paper. This option does not expect or
    allow a value.%
  }%
  \entry{\Option{twoside}}{%
    This option restricts the layer to two-sided printing. The default is for
    layers to appear in both one-sided and two-sided printing. This option
    does not expect or allow a value.%
  }%
  \entry{\ChangedAt{v3.18}{\Package{scrlayer}}%
    \Option{unrestricted}}{%
    This option removes all output restrictions. It is a combination of
    \Option{backandforeground}, \Option{everyside}, and
    \Option{floatornonfloatpage}. This option does not expect or allow a
    value.%
  }%
  \entry{\KOption{voffset}{\PName{length}}}{%
    Sets the distance of the layer from the top of the paper. How the distance
    is measured depends on the \Option{align} option. See the \Option{height}
    option for more information about valid expressions for \PName{length}.%
  }%
  \entry{\KOption{width}{\PName{length}}}{%
    Sets the width of the layer. See the \Option{height} option for more
    information about valid expressions for \PName{length}.%
  }%
\end{desclist}
%
\EndIndexGroup


\begin{Declaration}
  \Macro{ModifyLayers}\OParameter{option list}\Parameter{layer list}
\end{Declaration}
This\ChangedAt{v3.26}{\Package{scrlayer}} command executes
\DescRef{\LabelBase.cmd.ModifyLayer} with the given \PName{option list} for
all layers of the comma-separated layer list. Therefore the option can be used
to change attributes of several layers simultaneously.%
\EndIndexGroup


\begin{Declaration}
  \Macro{layerhalign}%
  \Macro{layervalign}%
  \Macro{layerxoffset}%
  \Macro{layeryoffset}%
  \Macro{layerwidth}%
  \Macro{layerheight}%
\end{Declaration}
These commands are only valid in the \PName{code} specified with
\Option{contents}, \Option{addcontents}, or \Option{pretocontents}. In this
case, they contain the layer's actual alignment, position, and dimensions that
will be used for the output. However, this is not necessarily the actual
dimensions of the layer's contents, e.\,g., if the contents are oversized or
do not fill the layer completely.

The primary layer attribute \PValue{align} is mapped to
\Macro{layerhalign}\ChangedAt{v3.19}{\Package{scrlayer}} and
\Macro{layervalign}. The horizontal values \PValue{l} and \PValue{r} are
copied to \Macro{layerhalign}. The vertical values \PValue{t} and \PValue{b}
are copied to \Macro{layervalign}. The value \PValue{c}, which is both 
horizontal and vertical, is copied to both commands. If there are several
conflicting values for \PValue{align}, only the last one is copied. Thus the
resulting \Macro{layerhalign} is either \PValue{l}, \PValue{c}, or \PValue{r},
and the resulting \Macro{layervalign} is either \PValue{t}, \PValue{c}, or
\PValue{b}.

Redefining\textnote{Attention!} these instructions to change the values stored
in them is not permitted, as it would lead to unpredictable results.%
\EndIndexGroup


\begin{Declaration}
  \Macro{LenToUnit}\Parameter{length}
\end{Declaration}
This\ChangedAt{v3.19}{\Package{scrlayer}} command originally came from
\Package{eso-pic}\IndexPackage{eso-pic}~2.0f. It converts lengths into
multiples of \Length{unit length} and can therefore be used everywhere \LaTeX{}
expects \Environment{picture} coordinates or \Length{unit length}-dependent
values. For more information, see \cite{package:eso-pic} and the descriptions
of \Macro{putUR}, \Macro{putLL}, and \Macro{putLR} below. If the command is 
already defined, e.\,g., by loading \Package{eso-pic} before
\Package{scrlayer}, the package does not define it again.%
\iffalse% Umbruchkorrekturtext
\par
It should be noted at this point that using package
\Package{picture}\IndexPackage{picture}\textnote{\Package{picture}} (see
\cite{package:picture}) supersedes \Macro{LenToUnit} more or less. The package
extends environment \Environment{picture} and the picture commands so that you
can use \LaTeX{} lengths directly for coordinates.%
\fi
\EndIndexGroup


\begin{Declaration}
  \Macro{putUL}\Parameter{content}%
  \Macro{putUR}\Parameter{content}%
  \Macro{putLL}\Parameter{content}%
  \Macro{putLR}\Parameter{content}%
  \Macro{putC}\Parameter{content}
\end{Declaration}
You\ChangedAt{v3.19}{\Package{scrlayer}} can use these commands inside the
value of \PValue{contents} layer option if the layer is declared with
\OptionValue{mode}{picture}. In this case, \Macro{putUL} places the
\PName{content} relative to the upper left corner of the layer and therefore
is the same as
\lstinline[breaklines=false]|\put(0,\LenToUnit{\layerheight})|. \Macro{putUR}
places the \PName{content} relative to the upper right corner of the layer and
therefore is the same as
\lstinline[breaklines=false]
|\put(\LenToUnit{\layerwidth},\LenToUnit{\layerheight})|.
\Macro{putLL} places the \PName{content} relative to the lower left corner of
the layer and therefore is the same as
\lstinline[breaklines=false]|\put(0,0)|. \Macro{putLR} places the
\PName{content} relative to the lower right corner and therefore is the same
as \lstinline[breaklines=false]|\put(\LenToUnit{\layerwidth},0)|. Last but
not least, \Macro{putC} places the \PName{content} relative to the centre of
the layer.%
\begin{Example}
  You want to determine exactly how accurately
  \OptionValueRef{typearea}{DIV}{classic} sets the height of the text area to
  the width of the page size. You declare a layer that both borders the text
  area and places a circle with a diameter of the paper width in the centre of
  the text area:
\begin{lstcode}
  \documentclass[DIV=classic]{scrartcl}
  \usepackage{pict2e}
  \usepackage{scrlayer}
  \DeclareNewLayer[%
    textarea,background,mode=picture,
    contents={%
      \putLL{\line(1,0){\LenToUnit{\layerwidth}}}%
      \putLR{\line(0,1){\LenToUnit{\layerheight}}}%
      \putUR{\line(-1,0){\LenToUnit{\layerwidth}}}%
      \putUL{\line(0,-1){\LenToUnit{\layerheight}}}%
      \putC{\circle{\LenToUnit{\paperwidth}}}%
    }
  ]{showtextarea}
  \DeclareNewPageStyleByLayers{test}{showtextarea}
  \pagestyle{test}
  \begin{document}
  \null
  \end{document}
\end{lstcode}
  You will notice that \Package{typearea}'s mapping to an integer \PName{DIV}
  value is very accurate in this example.
\end{Example}
Incidentally, you will find more information about late medieval book-page
canon sketched in the example in \autoref{sec:typearea.circleConstruction},
\autopageref{sec:typearea.circleConstruction}.

The \Macro{DeclareNewPageStyleByLayers}\IndexCmd{DeclareNewPageStyleByLayers}
command just used in the example defines a new page style using the newly
declared layer. It will be explained in \autoref{sec:scrlayer.pagestyles},
\DescPageRef{scrlayer.cmd.DeclareNewPageStyleByLayers}.%
\EndIndexGroup


\begin{Declaration}
  \Macro{GetLayerContents}\Parameter{layer~name}
\end{Declaration}
This\ChangedAt{v3.16}{\Package{scrlayer}} command returns the whole contents
of a layer. It is important to note\textnote{Attention!} that using this
command inside the \PName{code} of the layer attributes \Option{contents},
\Option{addcontents}, or \Option{pretocontents} can result in
infinite recursion when referencing the contents of the current layer. You
are responsible for avoiding such situations!%
\EndIndexGroup


\begin{Declaration}
  \Macro{IfLayerExists}\Parameter{layer~name}
                       \Parameter{then-code}\Parameter{else-code}
\end{Declaration}
This command can be used to execute code depending on whether or not a layer
with the specified \PName{layer name} exists. If the layer exists, the
\PName{then-code} will be executed; otherwise, the \PName{else-code} will be
executed. Note that the command cannot really test whether a layer exists.
Instead it uses a heuristic which will never yield a false negative but which,
in extreme cases, could yield a false positive.
\iffalse% Umbruchvarianten
Nevertheless, if the test yields a false positive, something has gone wrong.
For example, this could indicate an incompatible package or that the user is
doing something he or she should not.%
\else
False positives indicate a problem, such as the use of an incompatible package
or a bad choice of internal macro names by the user.
\fi
\EndIndexGroup


\begin{Declaration}
  \Macro{DestroyLayer}\Parameter{layer~name}
\end{Declaration}
If a layer with the given \PName{layer name} exists, all macros belonging to
it will be set to \Macro{relax}. In page styles already defined with
\Package{scrlayer}, such destroyed layers are ignored. Destroyed layers can be
redefined using \DescRef{\LabelBase.cmd.DeclareNewLayer} or
\DescRef{\LabelBase.cmd.ProvideLayer}, but they can no longer be changed using
\DescRef{\LabelBase.cmd.RedeclareLayer} or
\DescRef{\LabelBase.cmd.ModifyLayer}.%
\iffalse % See the note at the beginning of the end user interface section
\par
The command is intended to be used inside
\DescRef{\LabelBase.cmd.scrlayerOnAutoRemoveInterface} (see
\autoref{sec:scrlayer.enduserinterfaces},
\DescPageRef{scrlayer.cmd.scrlayerOnAutoRemoveInterface})
to remove layers defined using removable macros of an interface along with
that interface.%
\fi
\EndIndexGroup


\begin{Declaration}
  \OptionVName{draft}{simple switch}
  \Macro{layercontentsmeasure}%
\end{Declaration}
The \KOMAScript{} option \Option{draft} can be used to active the draft mode
of \Package{scrlayer}. The draft mode uses the \Macro{layercontentsmeasure}
command to print a ruler at each layer edge, of which the top and left one is
labelled in centimetres and the right and bottom one in inches. The rulers are
drawn behind the content of each layer. This command can also be used as
exclusive content of a layer.%
\EndIndexGroup


\section{Declaring and Managing Page Styles}
\seclabel{pagestyles}

\BeginIndexGroup
\BeginIndex{}{page>style}%
We now understand how to define and manage layers, but so far we do not know 
how they are used. The possibly surprising answer is, with page styles. In
\LaTeX{}, page styles usually define headers and footers of the page.

The header and footer of odd or right-hand pages\textnote{even or odd page}
are printed on pages with odd page numbers in two-sided printing or on all
pages in one-sided printing. This is directly comparable to the layer 
options\important[i]{\Option{evenpage}\\\Option{oddpage}} \Option{oddpage} and
\Option{evenpage}.

The page header\textnote{header or footer} is output before the main page
contents. The page footer is output after the main page contents. This
corresponds directly to the layer
options\important[i]{\Option{background}\\\Option{foreground}}
\Option{background} and \Option{foreground}.

Therefore it makes sense to define page styles as lists of layers. But instead
of just the four options mentioned above, you can use all the properties
explained in \autoref{sec:scrlayer.layers}, \autoref{tab:scrlayer.layerkeys}, 
on \autopageref{tab:scrlayer.layerkeys}.

As a result of these considerations, layer page
styles\textnote{layer page style}\Index{page style>layer}%
\Index{layer>page style}\Index{page>style} are one type of page style that 
\Package{scrlayer} provides. A layer page style consists of layers as well as
several hooks. The layers have already been described in
\autoref{sec:scrlayer.layers}. The hooks\Index[indexmain]{hooks}%
\textnote{hooks} are points in the expansion or execution of page styles to
which you can add code. Experienced users already know this concept from
commands like \Macro{AtBeginDocument} (see \cite{latex:usrguide}) or
\DescRef{scrlfile.cmd.BeforeClosingMainAux} (see
\DescPageRef{scrlfile.cmd.BeforeClosingMainAux}).

Page-style aliases are another type of page style which \Package{scrlayer}
provides. A page-style alias is actually a different page style. In other
words, the name of a page-style alias is an alternative name for another
page-style alias or for a page style. As a result, manipulating a page-style
alias results in manipulating the original page style. If the original page
style is itself an alias, its manipulation again results in the manipulation
of the alias's original page style, and so on until a real page style is
finally changed. The term \emph{real page style}\textnote{real page style} is
used to distinguish it from a page-style alias. All page styles that are not
page-style aliases are real page styles. Aliases can be defined for all page
styles, not just those defined with \Package{scrlayer}.

\begin{Declaration}
  \Macro{currentpagestyle}
  \Macro{toplevelpagestyle}
\end{Declaration}
The \Package{scrlayer} package patches the \DescRef{maincls.cmd.pagestyle}
command so that it sets \Macro{currentpagestyle} to the currently active page
style. Note that \DescRef{maincls.cmd.thispagestyle} does not change
\Macro{currentpagestyle}. If you use \DescRef{maincls.cmd.thispagestyle},
however, \Macro{currentpagestyle} can change within the \LaTeX{} output
routine. However, this change will only occur if \Macro{currentpagestyle} has
been actively protected from expansion until the execution of the output
routine.

Note that the layer page styles described later in this section do not rely on
this \DescRef{maincls.cmd.pagestyle} extension because they redefine
\Macro{currentpagestyle} themselves. This patch was made so that other,
non-\Package{scrlayer} page styles can use \Macro{currentpagestyle}.
Additionally, \Macro{currentpagestyle} is empty after loading
\Package{scrlayer} and before using \DescRef{maincls.cmd.pagestyle} for the
first time. Therefore, when defining an end-user interface, you may find it
useful to set the current page style to a default with an implicit
\DescRef{maincls.cmd.pagestyle} statement.

If \DescRef{maincls.cmd.pagestyle} activates an alias page style,
\Macro{currentpagestyle} shows not the alternative name but the name of
the real page style. You\ChangedAt{v3.16}{\Package{scrlayer}} can get the
alternative name using \Macro{toplevelpagestyle}. However, it is not
recommended to define page styles that produce different results depending on
\Macro{toplevelpagestyle}, e.\,g., using \DescRef{scrbase.cmd.Ifstr}. If you
were to activate such a page style using \DescRef{maincls.cmd.thispagestyle}
you could get the wrong result.%
\EndIndexGroup


\begin{Declaration}
  \Macro{BeforeSelectAnyPageStyle}\Parameter{code}%
  \Macro{AfterSelectAnyPageStyle}\Parameter{code}%
\end{Declaration}
The \Macro{BeforeSelectAnyPageStyle} command adds \PName{code} to the hook%
\textnote{hook} that will be executed inside \DescRef{maincls.cmd.pagestyle},
just before the page style is selected. Within the \PName{code}, you can use
\texttt{\#1} as a place-holder for the argument of
\DescRef{maincls.cmd.pagestyle}.

The \Macro{AfterSelectAnyPageStyle} command works similarly, but the
\PName{code} will be executed just after the page style has been selected and
after \DescRef{\LabelBase.cmd.currentpagestyle} has been set to the name of
the real page style.

Note\textnote{Attention!} that the \PName{code} of both commands is executed
only if a page style is selected with \DescRef{maincls.cmd.pagestyle} and not
if it is chosen in a different way, e.\,g., using
\DescRef{maincls.cmd.thispagestyle}. Note also that you cannot remove
\PName{code} from the hook after adding it. But the \PName{code} will be added
locally, so you can use a group to limit the scope of the \PName{code}.%
\EndIndexGroup


\begin{Declaration}
  \Macro{DeclarePageStyleAlias}\Parameter{page~style~alias~name}
                               \Parameter{original~page~style~name}
  \Macro{DeclareNewPageStyleAlias}\Parameter{page~style~alias~name}
                                  \Parameter{original~page~style~name}
  \Macro{ProvidePageStyleAlias}\Parameter{page~style~alias~name}
                               \Parameter{original~page~style~name}
  \Macro{RedeclarePageStyleAlias}\Parameter{page~style~alias~name}
                                 \Parameter{original page style name}
\end{Declaration}
\BeginIndex{}{page style>alias}%
\BeginIndex{}{alias>page style}%
These commands can be used to define a page style with name \PName{page style
  alias name} that is simply an alias for an existing page style with the
name \PName{original page style name}. If there is already a page style
\PName{page style alias name}, using \Macro{DeclarePageStyleAlias} or
\Macro{RedeclarePageStyleAlias} will destroy the alias before recreating it.

\Macro{DeclareNewPageStyleAlias} will throw an error message if a page style
\PName{page style alias name} has already been defined. It does not matter if
the previously defined page style is a layer-page style, a page style alias,
or another page style.

\Macro{ProvidePageStyleAlias} will define the alias only if the
\PName{page style alias name} page style has not been defined before. If the
\PName{page style alias name} page style already exists, nothing will be done.

\Macro{RedeclarePageStyleAlias} expects an existing
\PName{page style alias name} page style. It will destroy that page style and
afterwards define the alias. If the \PName{page style alias name} page style
does not exist, you will get an error.%
\iffree{\csname @tempswafalse\endcsname}{\csname @tempswatrue\endcsname}%
\csname if@tempswa\endcsname% Umbruchkorrekturtext
  \begin{Example}
    Suppose you write a class and use the \PageStyle{chapter} page style for the
    first page of each chapter. By default, this page style should match the
    \PageStyle{plain} page style. Therefore, you can use the \Package{scrlayer}
    package and use
\begin{lstcode}
  \DeclareNewPageStyleAlias{chapter}{plain}
\end{lstcode}
    to define the \PageStyle{chapter} page style as an alias for the
    \PageStyle{plain} page style. If, on the other hand, you later decide that
    the \PageStyle{chapter} plage style should correspond to the
    \PageStyle{empty} page style, you can achieve this with:
\begin{lstcode}
  \RedeclarePageStyleAlias{chapter}{empty}
\end{lstcode}%
  \end{Example}%
\fi
\EndIndexGroup


\begin{Declaration}
  \Macro{DestroyPageStyleAlias}\Parameter{page~style~name}%
\end{Declaration}
\BeginIndex{}{page style>alias}%
\BeginIndex{}{alias>page style}%
This command renders the page style named \PName{page style name} undefined
for \LaTeX{} if it is an alias for another page style. Afterwards, the page
style can be newly defined with
\DescRef{\LabelBase.cmd.DeclareNewPageStyleAlias} or
\DescRef{\LabelBase.cmd.ProvidePageStyleAlias}.%
\iffalse % See the note at the beginning of the end user interface section
\par
This command is intended to be used inside the argument code of
\DescRef{\LabelBase.cmd.scrlayerOnAutoRemoveInterface} to remove page styles
that have been declared as part of an end-user interface when removing this
interface automatically.%
\fi%
\EndIndexGroup


\begin{Declaration}
  \Macro{GetRealPageStyle}\Parameter{page~style~name}%
\end{Declaration}
\BeginIndex{}{page style>alias}%
\BeginIndex{}{alias>page style}%
This command will result in the (recursive) real page name of the page style
if \PName{page style name} is an alias of another page style. In all other
cases, even if there's no alias and no page style named \PName{page style
  name}, the result is simply \PName{page style name}. The command is fully
expandable and may be used, e.g., in the second argument of \Macro{edef}.%
\EndIndexGroup


\begin{Declaration}
  \Macro{DeclarePageStyleByLayers}\OParameter{option list}
                                  \Parameter{page style name}
                                  \Parameter{layer list}
  \Macro{DeclareNewPageStyleByLayers}\OParameter{option list}
                                     \Parameter{page style name}
                                     \Parameter{layer list}
  \Macro{ProvidePageStyleByLayers}\OParameter{option list}
                                  \Parameter{page style name}
                                  \Parameter{layer list}
  \Macro{RedeclarePageStyleByLayers}\OParameter{option list}
                                    \Parameter{page style name}
                                    \Parameter{layer list}
\end{Declaration}
\BeginIndex{}{page style>layers}%
\BeginIndex{}{layers>page style}%
These commands declare a page style named \PName{page style name}. The page
style will consist of the layers given in \PName{layer list}, a comma
separated list of layer names. Note\textnote{Attention!} that the \PName{page
  style name} and the layer names in the \PName{layer list} must be fully
expandable and should expand to letters. Several other characters are also
accepted, but their use is recommended only for experienced users.

The \PName{option list} is a comma-separated list of options in the form
\texttt{\PName{key}=\PName{value}}. These options may be used to set
additional features. Currently they are used to set the code that should be
expanded or executed at several hooks\Index{hooks}. See the introduction to
this section for more general information about hooks. See
\autoref{tab:scrlayer.pagestyle.hooks} for detailed information on specific
hooks.

\begin{desclist}
  \desccaption{%
    Hook options for page styles (in order of
    execution)\label{tab:scrlayer.pagestyle.hooks}%
  }{%
    Hook options for page styles (\emph{continued})%
  }%
  \entry{\OptionVName{onselect}{code}}{%
    The \PName{code} of this hook\Index{hook} is executed whenever the page
    style is selected, for example with \DescRef{maincls.cmd.pagestyle}. Note
    that \DescRef{maincls.cmd.thispagestyle} itself does not directly select a
    page style. In this case, the page style is only activated within \LaTeX's
    output routine.%
  }%
  \entry{\OptionVName{oninit}{code}}{%
    The \PName{code} of this hook\Index{hook} is executed whenever the output
    of the page style's layers is initialised. Note that this happens twice
    for each page: once for background layers and once for foreground layers.%
  }%
  \entry{\OptionVName{ononeside}{code}}{%
    The \PName{code} of this hook\Index{hook} is executed whenever the output
    of the page style's layers in one-sided printing is initialised. Note that
    this happens twice for each page: once for background layers and once for
    foreground layers.%
  }%
  \entry{\OptionVName{ontwoside}{code}}{%
    The \PName{code} of this hook\Index{hook} is executed whenever the output
    of the page style's layers in two-sided printing is initialised. Note that
    this happens twice for each page: once for background layers and once for
    foreground layers.%
  }%
  \entry{\OptionVName{onoddpage}{code}}{%
    The \PName{code} of this hook\Index{hook} is executed whenever the output
    of the page style's layers on an odd page is initialised. Note that this
    happens twice for each page: once for background layers and once for
    foreground layers. Note also that in one-sided printing all pages are odd
    pages, not just those with odd page numbers.%
  }%
  \entry{\OptionVName{onevenpage}{code}}{%
    The \PName{code} of this hook\Index{hook} is executed whenever the output
    of the page style's layers on an even page is initialised. Note that this
    happens twice for each page: once for background layers and once for
    foreground layers. Note also that in one-sided printing there are no even
    pages. Instead, all pages are treated as odd pages, not just those with
    odd page numbers.%
  }%
  \entry{\OptionVName{onfloatpage}{code}}{%
    The \PName{code} of this hook\Index{hook} is executed whenever the output
    of the page style's layers on a float page is initialised. Note that this
    happens twice for each page: once for background layers and once for
    foreground layers. Note also that float pages are only those pages with
    one or more p-placed floating environments.%
  }%
  \entry{\OptionVName{onnonfloatpage}{code}}{%
    The \PName{code} of this hook\Index{hook} is executed whenever the output
    of the page style's layers on a non-float page is initialised. Note that
    this happens twice for each page: once for background layers and once for
    foreground layers. Note also that float pages are only the pages on which
    one or more p-placed floating environments are output. Other pages may
    well have t-, h-, or b-placed floating environments.%
  }%
  \entry{\OptionVName{onbackground}{code}}{%
    The \PName{code} of this hook\Index{hook} is executed whenever the output
    of the page style's background layers is initialised. Note that this
    happens once each page.%
  }%
  \entry{\OptionVName{onforeground}{code}}{%
    The \PName{code} of this hook\Index{hook} is executed whenever the output
    of the page style's foreground layers is initialised. Note that this
    happens once each page.%
  }%
\end{desclist}

\iffalse% Umbruchvarianten
  While the \Macro{DeclarePageStyleByLayers} command always defines the page
  style, \Macro{DeclareNewPageStyleByLayers} generates an error message if a
  page style with the same name already exists. Note\textnote{Attention!} that
  the declaration of a page style that is already an alias for another page
  style (see, for example, \Macro{DeclareAliasPageStyle} earlier in this
  section) will redefine not the specified page style alias but the real page
  style (see \DescRef{\LabelBase.cmd.GetRealPageStyle} earlier in this
  section).%
\else%
  The \Macro{DeclarePageStyleByLayers} command defines the page style
  regardless of whether a page style of \PName{page style name} already
  exists. If necessary, the existing page style is completely
  redefined. However, if a page style alias \PName{page style name} already
  exists, the associated real page style, not the page style alias itself, is
  redefined (see \DescRef{\LabelBase.cmd.GetRealPageStyle} earlier in this
  section).

  The \Macro{DeclareNewPageStyleByLayers} command differs if a page style of
  the same name already exists. Regardless of whether it is a real or an alias
  page style, an error will be reported in this case.
\fi

In contrast, \Macro{ProvidePageStyleByLayers} preserves the page style
unchanged if a page style with name \PName{page style name} already exists. If
no such page style exists, it is defined as in
\Macro{DeclarePageStyleByLayers}.

The \Macro{RedeclarePageStyleByLayers} in turn expects that a page style of
of the name \PName{page style name} already exists and then redefines its real
page style. However, if no page style of the specified name exists, an error
message results.

Also note the remarks below about the pseudo-page style
\PageStyle{@everystyle@}.%
\EndIndexGroup


\begin{Declaration}
  \PageStyle{@everystyle@}%
  \PageStyle{empty}
\end{Declaration}
\BeginIndex{}{page style>layers}%
\BeginIndex{}{layers>page style}%
The \Package{scrlayer} package defines two specific page styles worth noting.
The first of these is \PageStyle{@everystyle@}%
\important{\PageStyle{@everystyle@}}. This page style should never be used
like a normal page style, for example with \DescRef{maincls.cmd.pagestyle} or
\DescRef{maincls.cmd.thispagestyle}, or as the target of a page-style alias.
Instead, the layers and hooks\Index{hooks} of this page style are used by all
other layer page styles. The hooks of \PageStyle{@everystyle@} are placed in
front of their respective hooks, and the layers in front of the respective
layers, of the active page style.

Thus adding a layer to the pseudo-page style \PageStyle{@everystyle@} or code
to a hook of this page style is like adding a layer or hook code to all layer
page styles, even the empty one. There's one crucial difference: commands that
reference the layers of a page style which include
\DescRef{\LabelBase.cmd.ForEachLayerOfPageStyle}, e.\,g., the commands
\DescRef{\LabelBase.cmd.AddLayersToPageStyleBeforeLayer} or
\DescRef{\LabelBase.cmd.AddLayersToPageStyleAfterLayer}, disregard the layers
of the page style \PageStyle{@everystyle@} when applied to a different layer
page style.

The second, slightly different page style is \PageStyle{empty}. Normally the
\LaTeX{} kernel defines the \PageStyle{empty} page style to have an empty
header and footer. The \Package{scrlayer} package redefines this page style as
a layerless page style. Nonetheless, you can use it like any other layer page
style. The main advantage of the layer page style over the original page
style from the \LaTeX{} kernel is that it also executes the hooks and layers
of the psuedo-layer page style \PageStyle{@everystyle@}.%
\EndIndexGroup


\begin{Declaration}
  \OptionVName{onpsselect}{code}%
  \OptionVName{onpsinit}{code}%
  \OptionVName{onpsoneside}{code}%
  \OptionVName{onpstwoside}{code}%
  \OptionVName{onpsoddpage}{code}%
  \OptionVName{onpsevenpage}{code}%
  \OptionVName{onpsfloatpage}{code}%
  \OptionVName{onpsnonfloatpage}{code}%
  \OptionVName{onpsbackground}{code}%
  \OptionVName{onpsforeground}{code}
\end{Declaration}
\BeginIndex{}{page style>layers}%
\BeginIndex{}{layers>page style}%
There is also a \KOMAScript{} option for each of the hooks\Index{hooks} in
\autoref{tab:scrlayer.pagestyle.hooks}%
\iftrue
. The names of the \KOMAScript{} options are similar to those for declaring
page style layers, except that a ``\texttt{ps}'' is inserted after
``\texttt{on}'' at the beginning of the name
\else
, into the names of which a ``\texttt{ps}'' is inserted
\fi
. The values of these \KOMAScript{} options are used as the initial values for
the corresponding hooks. These initial values are then extended by all the
values assigned to the corresponding hooks in the \PName{option list} of the
declaration commands. You can remove the default with
\DescRef{\LabelBase.cmd.ModifyLayerPageStyleOptions}, which is explained later
in this section.%
\EndIndexGroup


\begin{Declaration}
  \OptionVName{singlespacing}{simple switch}
\end{Declaration}
If\ChangedAt{v3.24}{\Package{scrlayer}\and \Package{scrlayer-scrpage}} a
document is printed with increased line spacing, e.\,g., using the
\Package{setspace}\IndexPackage{setspace}\important{\Package{setspace}}
package, it is often undesirable for the header and footer to be printed with
this increased spacing. This is particularly true if the header and footer
consist of only a single line. In this case you can use \KOMAScript{} option
\Option{singlespacing}. However, the default\textnote{default} is
\OptionValue{singlespacing}{false}! The option generally applies to all layer
page styles. If you want single-spacing for only some page styles, use
\OptionValue{oninit}{\Macro{linespread}\PParameter{1}\Macro{selectfont}} for
those page styles.%
\EndIndexGroup


\begin{Declaration}
  \OptionVName{deactivatepagestylelayers}{simple switch}%
  \Macro{ForEachLayerOfPageStyle}\Parameter{page style name}\Parameter{code}%
  \Macro{ForEachLayerOfPageStyle*}\Parameter{page style name}\Parameter{code}
\end{Declaration}
\BeginIndex{}{page style>layers}%
\BeginIndex{}{layers>page style}%
As long as the \KOMAScript{} option \Option{deactivatepagestylelayers} is not
enabled, the \Macro{ForEachLayerOfPageStyle} command can execute arbitrary
\PName{code} for each layer of the page style named \PName{page style name}.
Inside of \PName{code}, the place holder \PValue{\#1} serves as a
reference to the name of the current layer.
\begin{Example}
  If you want to print the names of all layers of the \PValue{scrheadings}
  page style as a comma-separated list, you can use:
\begin{lstcode}
  \let\commaatlist\empty
  \ForEachLayerOfPageStyle{scrheadings}{%
    \commaatlist#1\gdef\commaatlist{, }}
\end{lstcode}
\end{Example}
In\textnote{Attention!} the example above, we had to use \Macro{gdef} instead
of \Macro{def} because \Macro{ForEachLayerOfPageStyle} executes the 
\PName{code} inside a group to minimise side effects. However, \Macro{gdef}
redefines \Macro{commaatlist} globally so the change will persist when the
\PName{code} for the next layer is executed.

Alternatively,\ChangedAt{v3.18}{\Package{scrlayer}} you can use \Macro{def}
with the starred variant \Macro{ForEachLayerOfPageStyle*}. This form dispenses
with the extra group when executing \PName{code}. However, the user then has
to take make sure that the \PName{code} has no unwanted side effects. In
particular, deactivating all layers using
\OptionValue{deactivatepagestylelayers}{true} within \PName{code} would
persist beyond the call to \Macro{ForEachLayerOfPageStyle*}.

Various \Package{scrlayer} commands also use \Macro{ForEachLayerOfPageStyle}
internally. Their behaviour can therefore also be changed using the
\KOMAScript{} option \Option{deactivatepagestylelayers}. With this option,
you can temporarily disable and thus hide all layers of all layer page
styles.%
\EndIndexGroup


\begin{Declaration}
  \Macro{AddLayersToPageStyle}%
  \Parameter{page style name}\Parameter{layer list}%
  \Macro{AddLayersAtBeginOfPageStyle}%
  \Parameter{page style name}\Parameter{layer list}%
  \Macro{AddLayersAtEndOfPageStyle}%
  \Parameter{page style name}\Parameter{layer list}%
  \Macro{RemoveLayersFromPageStyle}%
  \Parameter{page style name}\Parameter{layer list}%
\end{Declaration}
\BeginIndex{}{page style>layers}%
\BeginIndex{}{layers>page style}%
You can use these commands to add layers to a layer page style or to remove
layers from a layer page style. The page style is referenced by its
\PName{page style name}. The layers are given by a comma-separated
\PName{layer list}.

Both the \Macro{AddLayersToPageStyle} and the
\Macro{AddLayersAtEndOfPageStyle}\textnote{add at the end} commands insert the
new layers at the bottom of the page style's layer list. Logically, the newly
added layers lie above or in front of the old layers. Background layers, of
course, still are logically behind the text layer and thus behind all
foreground layers.

In contrast, the \Macro{AddLayersAtBeginOfPageStyle}\textnote{add at the
  beginning} command inserts the new layers at the top of the page style's
layer list. The layers are separately inserted to the top of the list in the
same order they appear in the \PName{layer list} parameter. This means that
the last layer in the \PName{layer list} parameter will become the first, and
thus the lowest, layer of the page style.

\iffalse% Umbruchkorrekturtext (beim Aktiveren muss unten \textnote{remove}
% entfernt werden!)
The \Macro{RemoveLayersFromPageStyle} command is exactly the opposite. It
removes\textnote{remove} the specified page-style levels.%
\fi

The \Macro{RemoveLayersFromPageStyle}\textnote{remove} command removes layers
from the layer list of the page style named \PName{page style name}.
Attempting to remove layers which are not part of the page style's layer list
will be ignored. But attempting to add layers to or remove layers from a page
style that is neither a layer page style nor a page-style alias is an error
and will be reported as such.%
\EndIndexGroup


\begin{Declaration}
  \Macro{AddLayersToPageStyleBeforeLayer}%
  \Parameter{page style name}\Parameter{layer list}%
  \Parameter{reference layer name}%
  \Macro{AddLayersToPageStyleAfterLayer}%
  \Parameter{page style name}\Parameter{layer list}%
  \Parameter{reference layer name}
\end{Declaration}
\BeginIndex{}{page style>layers}%
\BeginIndex{}{layers>page style}%
\iffalse% Umbruchvarianten
These two commands are similar to the previous ones, but they take an
additional parameter,  \Parameter{reference layer name}. The layer list of
the page style named in \Parameter{page style name} is searched for this
reference layer. %
\else%
These commands are similar to the previous ones. The existing layers of the
page style, however, are searched for the \PName{reference layer name}. %
\fi%
The layers in the \Parameter{layer list} parameter are then inserted
before\textnote{add before/after layer} or after this reference layer%
\iffalse% Umbruchkorrekturtext
in the layers of the page style%
\fi%
. The order of the layers in the \PName{layer list} is retained.

If the reference layer named \PName{reference layer name} is not part of the
given page style, nothing is inserted. On the other hand, if the page style is
neither a layer page style nor a page-style alias, an error will be reported.%
\EndIndexGroup


\begin{Declaration}
  \Macro{UnifyLayersAtPageStyle}\Parameter{page style name}
\end{Declaration}
\BeginIndex{}{page style>layers}%
\BeginIndex{}{layers>page style}%
The commands for defining page styles or adding layers to a page style do not
care how many times a layer appears in a page style, so it is quite
permissible for a layer to appear multiple times. In most cases, however, it
does not make sense to use the same layer several times in one page style.
Therefore, you can use \Macro{UnifyLayersAtPageStyle} to remove all layer
duplicates from the layer page style of the specified \Parameter{page style
	name}.

Note\textnote{Attention!} that this function can change the order of layers.
So if you need a specific order, you should remove all layers and add the
layers in the order you want instead of using \Macro{UnifyLayersAtPageStyle}.%
\EndIndexGroup


\begin{Declaration}
  \Macro{ModifyLayerPageStyleOptions}%
  \Parameter{page style name}\Parameter{option list}%
  \Macro{AddToLayerPageStyleOptions}%
  \Parameter{page style name}\Parameter{option list}
\end{Declaration}
\BeginIndex{}{page style>layers}%
\BeginIndex{}{layers>page style}%
These two commands can be used to modify the options, and thus the
hooks\Index{hooks}, of a layer page style. With
\Macro{ModifyLayerPageStyleOptions}\textnote{change page-style options}, only
the options in the comma-separated \PName{option list} will be set to the new
values given there. The previous values are lost. All options from
\autoref{tab:scrlayer.pagestyle.hooks},
\autopageref{tab:scrlayer.pagestyle.hooks} are allowed. Options or hooks that
are not specified in the \PName{option list} will remain unchanged. If you
want to set an option to do nothing you can set it to the value \Macro{relax}.
Setting an option to a new value using \Macro{ModifyLayerPageStyleOptions}
will remove the previous value, including the global default value. This
statement is the only way to remove the global defaults of the \KOMAScript{}
options from a page style.

\Macro{AddToLayerPageStyleOptions}\textnote{extend page-style options}, on the
other hand, does not overwrite the previous values. Instead it adds\,---\,or,
more precisely, concatenates\,---\, the new values to old ones.%
\EndIndexGroup


\begin{Declaration}
  \Macro{IfLayerPageStyleExists}%
  \Parameter{page style name}\Parameter{then code}\Parameter{else code}%
  \Macro{IfRealLayerPageStyleExists}%^
  \Parameter{page style name}\Parameter{then code}\Parameter{else code}%
\end{Declaration}
\BeginIndex{}{page style>layers}%
\BeginIndex{}{layers>page style}%
With these commands, you can execute code depending on whether a page style is
a layer page style or not. The \Macro{IfLayerPageStyleExists} command executes
the \PName{then code} if \PName{page style name} is the name of a layer page
style or a page-style alias that results in a layer page style. Otherwise, the
command executes the \PName{else code}. Internally, this command is often used
to throw an error message if you use one of the layer page style commands with
an \PName{page style name} that does not correspond to a layer page style.

The \Macro{IfRealLayerPageStyleExists} command goes one step further and
executes the \PName{then code} only if the page style specified by \PName{page
  style name} is itself a layer page style. So if \PName{page style name} is a
page-style alias, this command executes the \PName{else code} even if the
alias resolves to a real layer page style.%
\EndIndexGroup


\begin{Declaration}
  \Macro{IfLayerAtPageStyle}%
  \Parameter{page style name}\Parameter{layer name}%
  \Parameter{then code}\Parameter{else code}%
  \Macro{IfSomeLayerAtPageStyle}%
  \Parameter{page style name}\Parameter{layer list}%^
  \Parameter{then code}\Parameter{else code}%
  \Macro{IfLayersAtPageStyle}%
  \Parameter{page style name}\Parameter{layer list}%
  \Parameter{then code}\Parameter{else code}%
\end{Declaration}
\BeginIndex{}{page style>layers}%
\BeginIndex{}{layers>page style}%
These commands can be used to test whether one or more layers are part of a
page style. The \Macro{IfLayerAtPageStyle} command expects exactly one
\PName{layer name}\textnote{exactly one layer} as the second argument. If this
layer is part of the page style specified in \PName{page style name}, the
\PName{then code} will be executed. Otherwise, the \PName{else code} will be
executed.

The \Macro{IfSomeLayerAtPageStyle} and \Macro{IfLayersAtPageStyle} commands
allow a comma-separated \PName{layer list}. \Macro{IfSomeLayerAtPageStyle}
will execute the \PName{then code} if \emph{at least one} of the layers in the
\PName{layer list} parameter is part of the layer list of \PName{page style
  name}. In contrast, \Macro{IfLayersAtPageStyle} executes the \PName{then
  code} only if \emph{all} the layers in the \PName{layer list} parameter are
part of the page style. If the condition is not met, the \PName{else code}
will be executed.

With suitable nesting of these commands, you can construct complex conditions.
If you use only one \PName{layer name} in the \PName{layer list}, all three
statements are synonymous.%
\EndIndexGroup


\begin{Declaration}
  \Macro{DestroyRealLayerPageStyle}\Parameter{page style name}
\end{Declaration}
\BeginIndex{}{page style>layers}%
\BeginIndex{}{layers>page style}%
\iftrue
This statement makes a layer page style undefined. If a page-style alias or
ordinary page style is specified, the command is ignored.
\else
With this command you can remove a the definition of a layer page style.
However, this only occurs if a layer page style named \PName{page style name}
exists. If, instead, it is a page-style alias, a different (non-layer) page
style, or not a page style at all, nothing happens; the command is ignored.%
\fi

If \PName{page style name} is the name of the current page style, the current
page style will becomes a kind of empty page style. If the page style set with
\DescRef{maincls.cmd.thispagestyle} is \PName{page style name}, it will simply
be reset. The previous \DescRef{maincls.cmd.thispagestyle} command loses its
current effect.

Note\textnote{Attention!} that the layers of the page style are not destroyed
automatically. If you want to destroy the layers too, you can do this with: 
\begin{lstcode}
  \ForEachLayerOfPageStyle{...}{\DestroyLayer{#1}}
\end{lstcode}
before destroying the layer page style itself.%
\iffalse % See the note at the beginning of the end user interface section
\par
The command is intended to be used within the \PName{code} argument of
\DescRef{\LabelBase.cmd.scrlayerOnAutoRemoveInterface} to remove page styles
that are defined as part of an end-user interface. See
\autoref{sec:scrlayer.enduserinterfaces} below for more information about
auto-removal code.%
\fi%
\EndIndexGroup
\EndIndexGroup

\LoadCommonFile{headfootheight}% \section{Height of Page Head and Foot}

\LoadCommonFile{pagestylemanipulation}% \section{Manipulation of Defined Page Styles}

\section{Defining and Managing Interfaces for End Users}
\seclabel{enduserinterfaces}

\iftrue% The whole mechanism is deprecated and should not be used any
       % longer. So the documentation is also deactivated.
% TODO: Fix new translation
Until version 3.27\ChangedAt{v3.28}{\Package{scrlayer}} package
\Package{scrlayer} provided mechanism to manage concurrent end user
interfaces. The mechanism has been marked as experimental and the usability
limited. Only \KOMAScript{} itself has used this mechanism and from version
3.28 it is marked as deprecated. So the commands
\Macro{scrlayerInitInterface}\IndexCmd{scrlayerInitInterface},
\Macro{scrlayerAddToInterface}\IndexCmd{scrlayerAddToInterface},
\Macro{scrlayerAddCsToInterface}\IndexCmd{scrlayerAddCsToInterface},
\Macro{scrlayerOnAutoRemoveInterface}\IndexCmd{scrlayerOnAutoRemoveInterface}%
\important{\Macro{scrlayerOnAutoRemoveInterface}}
and the options
\Option{forceoverwrite}\IndexOption{forceoverwrite},
\Option{autoremoveinterfaces}\IndexOption{autoremoveinterfaces}
should not be used any longer.%
% :ODOT
\else%
The \Package{scrlayer} package provides an experimental interface to define
and manage (concurrent) interfaces for end users. \iffree{In the long run,
  this interface may disappear from \Package{scrlayer} and be taken over by
  \Package{scrbase} instead.}{} Currently, this interface is highly
experimental%
\iffree{ and therefore \Package{scrlayer} provides these interface commands
  only for the use of subpackages of \Package{scrlayer}}{}%
. Given the current state of development, you should not depend on automatic
removal of a concurrent interface to work. Instead, you should avoid using
concurrent end-user interfaces.

This section only describes the interface commands for defining an end-user
interface. For end users themselves, it is of little interest. Rather, this
section is intended for authors of packages and classes that build on
\Package{scrlayer}. End users will find information about specific end-user
interfaces in \autoref{cha:scrlayer-scrpage},
\autoref{cha:scrlayer-scrpage-experts}, and \autoref{cha:scrlayer-notecolumn}.

\begin{Declaration}
  \Macro{scrlayerInitInterface}\OParameter{interface name}
\end{Declaration}
The \Macro{scrlayerInitInterface} command registers a new interface named
\PName{interface name}. The \PName{interface name} must be unique. If an
interface with the same name has already been registered, an error will occur.

This command should always appear as the first command when defining an
end-user interface and therefore is described here first. If the optional
argument\,---\,including the square brackets\,---\,is omitted,
\PValue{\Macro{@currname}.\Macro{@currext}} will be used instead. For classes
and packages, this is the file name of the class or package. But of course you
can use any other sequence of characters with a category of \emph{letter} or
\emph{other}. This is useful, for example, when a class or package defines
multiple end-user interfaces%
\EndIndexGroup


\begin{Declaration}
  \OptionVName{forceoverwrite}{simple switch}%
  \OptionVName{autoremoveinterfaces}{simple switch}%
  \Macro{scrlayerAddToInterface}%
  \OParameter{interface name}\Parameter{command}\Parameter{code}%
  \Macro{scrlayerAddCsToInterface}%
  \OParameter{interface name}\Parameter{command sequence}\Parameter{code}
\end{Declaration}
One of the special features of \Package{scrlayer}'s end user interfaces is
that they should register all interface-dependent commands (also known as
\emph{macros}). You can do this using \Macro{scrlayerAddToInterface}. The
optional argument \PName{interface name} must be an interface name previously
registered with \DescRef{\LabelBase.cmd.scrlayerInitInterface}. An error will
occur if the interface has not been initialised.

If\textnote{Attention!} your interface defines macros not just when the class
or package is being loaded but also at runtime, you must provide the interface
name in the optional argument even if it corresponds to the file name of the
class or package, since the values of \Macro{@currname} and \Macro{@currext}
are only valid while the class or package is being loaded.

The first mandatory argument is the \PName{command}\footnote{The
  \PName{command} consists of a backslash followed by a \PName{command
    sequence} that consists of characters of the category code \emph{letter},
  or of exactly one character of the category \emph{other}, or of a character
  of the category \emph{active} (without the backslash).} to be added to the
interface. If the command can be defined, this will be done. In addition, it
will set to \Macro{relax} and \PName{code} will be executed. Within
\PName{code}, you can then define \PName{command}, e.\,g., using
\Macro{newcommand}.

But when can a command be defined? If a command is undefined or \Macro{relax},
it can always be defined. If a command has already been defined \emph{and}
registered for another interface \emph{and} if the \KOMAScript{} option
\Option{autoremoveinterfaces} has been activated, the other interface will be
removed automatically, and the \PName{command} will be set to \Macro{relax}
and registered for the new interface specified. If a \PName{command} is
already defined but is \emph{not} part of another interface, \emph{and} if the
\KOMAScript{} option \Option{forceoverwrite} has been activated, the
\PName{command} is also set to \Macro{relax} and registered for the specified
interface. In all other cases, however, the command is not definable, in
particular if it is already defined and the \KOMAScript{} options
\Option{autoremoveinterfaces} and \Option{forceoverwrite} are deactivated.

The \Macro{scrlayerAddCsToInterface} command is similar to
\Macro{scrlayerAddToInterface} but it expects the first argument to be not a
\PName{command} but a command sequence\footnote{A command sequence must be
  fully expandable and its expansion must result in characters of the category
  code \emph{letter}, \emph{other}, or \emph{space}.}.%
\EndIndexGroup


\begin{Declaration}
  \Macro{scrlayerOnAutoRemoveInterface}%
  \OParameter{interface name}\Parameter{code}
\end{Declaration}
The \Macro{scrlayerOnAutoRemoveInterface} command registers \PName{code} to be
executed in the event that the end-user interface with the specified
\PName{interface name} is automatically removed (see
\DescRef{\LabelBase.option.autoremoveinterfaces} earlier in this section).
This can be used, for example, to automatically destroy layers or page styles
that rely on commands from the end-user interface (see
\DescRef{\LabelBase.cmd.DestroyLayer},
\DescRef{\LabelBase.cmd.DestroyPageStyleAlias}, and
\DescRef{\LabelBase.cmd.DestroyRealLayerPageStyle}). Regarding the default for
the optional argument, please refer to the explanation for
\DescRef{\LabelBase.cmd.scrlayerInitInterface}.%
\EndIndexGroup%
\fi%
%
\EndIndexGroup

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